The handling of food makes great demands on the packages in which the food is stored. They must fulfil sanitary requirements, i.e. bacteria and flavourings shall not be capable of migrating through the package to and from the surroundings. They must have enough strength for the handling at storage and transport. Strict environmental requirements are also put on the packages, e.g. concerning the recycling, composting or combustion of used packages.
Ready-cooked food is becoming increasingly common and besides functioning as a package for storing of the product, demands are made for a direct placement of the packages in microwave ovens and conventional ovens for the preparation of food dishes. Packages in the form of aluminium ware are now being used to a high extent. They withstand conventional ovens but a disadvantage is that they become very hot. Aluminium ware is also fragile and does not withstand high loads. Furthermore, it should not be placed in microwave ovens. Another common type of package is trays of foamed polyester. An essential disadvantage of foamed polyester is that they cannot be placed in a conventional oven since they may melt.